Thripinae, Thripidae, Terebrantia, Thysanoptera

Figures

Fig. 1: 8-segmented antenna, segments I-V and segments II-VI (asymmetric pedicel and simple sense cone on segments III and IV)
Fig. 2: Head dorsal with ocellar triangle
Fig. 3: Head ventral with mouthcone and sclerotized ommatidia
Fig. 4: Trapezoidal shape of pronotum
Fig. 5: Meso- and metanotum
Fig. 6: Meso- and metasternum
Fig. 7: Fore wing, distal area of fore wing
Fig. 8: Tergites IV and V
Fig. 9: Sternites VI and VII

Arorathrips mexicanus is a pest of grass-seeds. Female macropterous; dark brown when mature, but teneral individuals with abdomen pale; fore wings light brown with subbase pale. Antennae 8-segmented; segments III & IV with stout simple sense cone, II prolonged on external margin with a terminal sensorium (Fig. 1). Head small and projecting in front of eyes; 3 pairs of ocellar setae, pair III arise in front of ocellar triangle (Fig. 2 and 3). Pronotum trapezoidal with 2 pairs of posteroangular setae (Fig. 4). Metanotum with mainly equiangular reticulations; median pair of setae arise behind anterior margin; campaniform sensilla present (Fig. 5). Meso- and metafurca weakly developed and without median spinula (Fig. 6). Mid and hind tarsi 2-segmented; fore coxae enlarged and transverse; fore femora swollen (Fig. 3); fore tibia extending laterally along external margin of fore tarsus. Fore and hind wings present, more than half as long as abdomen (macropterous) or absent (apterous), fore wing slender and acute at apex; first vein with 2-3 setae on distal half; second vein with 3 of 4 widely spaced setae (Fig. 7). Tergites with many lines of sculpture medially; II-V with transverse row of small tubercles along antecostal ridge (Fig. 8); II-VIII with complete continuous craspedum. Ovipositor weakly developed and without teeth. Sternite VII median posteromarginal setae arise at amrgin (Fig. 9).
Male apterous, body color yellow; sternites III-VII with large circular glandular area medially.

The genus Arorathrips Bhatti, 1990
Members of this genus were originally included in the genus Chirothrips, and later seperated to it's current generic state by Bhatti (1990) with four species in which the fore tibia is prolonged at its apex around the external margin of the fore tarsus. The generic concept was subsequently extended (Mound & Marullo 1996) to include a total of 15 species, nearly all from the New World and all with the mesothoracic furca greatly reduced. Like species of Chirothrips, members of the genus Arorathrips have a small head, short antennae with 8 segments, antennal segment II mostly expanded laterally, and a trapezoidal pronotum with 2 pairs of elongate posteroangular setae. Moreover, all species of the genus Arorathrips lack multiple setae on the meso- and metanota and on the ventral surface of the head (Mound & Marullo 1996).

Similar to the large genus Chirothrips with 8-segmented antennae, antennal segment II expanded laterally, and trapezoidal pronotum with 2 pairs of elongate posteroangular setae. But Arorathrips mexicanus possesses a greatly reduced mesothoracic furca (furcal pits widely separated), the fore tibia is prolonged at its apex around the external margin of the first fore tarsal segment, and tergites II-V with a transverse row of small tubercles along antecostal ridge. Whereas all species of the genus Chirothrips have furcal pits on mesosternum fused in the middle line, the fore tibia is not prolonged around fore tarsal segment, and the sculpture of antecostal ridge on tergites II-V is more or less elongated. Compared to species of Chirothrips, in Arorathrips mexicanus median posteromarginal setae on sternite VII arising at margin, whereas in species of Chirothrips those setae arise in front of posterior margin of sternite VII.

Life history
As with other thrips species the life cycle from egg to adult is dependent on temperature. The full cycle can take about 15 days (Lewis 1973) to over a month and adults may live for more than one month producing several generations in one year depending on seasonal weather.

Host plants
Grasses-seeds (Poaceae).
Crops: pumpkins, rice, sorghum, tomato.
Weeds: Bidens pilosa, Galinsoga parviflora, Tagetes minuta.

Vector capacity
None identified, but possible mechanical distribution of phytopathogenic fungi and bacteria.

Damage and symptoms
-

Detection and control strategies
-

Additional notes
In this species, an adult female lays a few eggs within the floret of a grass, and the larva and then the pupa develop within this floret. As a result, commercial grass seed production can be decimated. This species is possibly spread as resting life stages within cultivated grass seeds when grasses are transported around the world.

Biogeography

In tropical and subtropical regions. Ethiopia (Sodere), Mozambique (Umbeluzi - southwest of Maputo, Machava - near Maputo), Nigeria (Samaru), South Africa (Gauteng: Pretoria, Kameeldrif, Silverton; Limpopo: Entabeni Forest Station - 4500 ft., Pietersburg - 4200 ft., Mokopane - 4500 ft., Zebediela - 3400 ft., Mariepskop - 4500 ft., Satara - Kruger National Park, Modimolle - 4600 ft., Bela Bela, Farm Kalkfontein, Pienaarsrivier - 3700 ft., Nelspruit - 2350 ft.; Mpumalanga: Kaapmuiden - 1350 ft., Nelspruit - 2350 ft.; KwaZulu-Natal: Pongola River east of Ingwavuma, Mposa and Dukuduku Forest), Uganda, Zimbabwe (Mutare - 3700 ft., Birchenough Bridge).

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